An agricultural baler is a trailed machine, typically towed behind agricultural vehicles such as tractors, used in agriculture for the purpose of forming bales of agricultural materials, such as straw, hay, silage or other biomass, produced during a harvesting or mowing operation. A baler typically comprises an infeed through which biomass is introduced into a bale-forming chamber. In the bale-forming chamber the biomass is generally compressed or otherwise treated to form bales. The completed bales are tied with twine or a similar lineal object or are packaged in another way to make them self-supporting. The bales are subsequently ejected by means of a discharge mechanism.
Referring to the drawings, FIG. 1 shows agricultural baler 600 comprising a frame 512 which is equipped with a forwardly extending tongue 514 at its front end with hitch means (not shown) for coupling the baler 600 to a towing tractor. A pick-up assembly 513 lifts windrowed agricultural material off the field as the baler 600 is travelled there over and delivers such material into the front end of a rear ward and upwardly curved, charge-forming feeder duct 515. The duct 515 communicates at its upper end with an overhead, fore-and-aft extending bale-forming chamber 516 into which agricultural material charges are loaded by a cyclically operating stuffer mechanism 517. A continuously operating packer mechanism 519 at the lower front end of the feeder duct 515 continuously feeds and packs material into the duct 515 as to cause charges of the agricultural material to take on and assume the internal configuration of the duct 515 prior to periodic engagement by the stuffer 517 and insertion up into the bale-forming chamber 516. The feeder duct 515 may be equipped with means (not illustrated) for establishing whether a complete charge has been formed therein and operating the stuffer mechanism 517 in response thereto. Each action of the stuffer mechanism 517 introduces a “charge” or “flake” of agricultural material from the duct 515 into the chamber 516. A plunger 562 reciprocates in a fore-and-aft direction within the bale-forming chamber 516. Biomass fed via the feeder duct 515 is thereby compacted, e.g. compressed or otherwise treated, so as to form bales in the above-described operation of the agricultural baler 600. Rectangular bales are formed. The completed bales are tied with twine or a similar lineal object to make them self-supporting, for example for shipping and storage. Once tied, the bales are discharged from the rear end of the bale-forming chamber 516 onto a discharge in the form of a chute, generally designated 520.
In the art the load on the plunger is either measured by load sensors or sensors that measure deformation of the bale chamber. Those sensors are expensive or require a complex set-up with careful calibration because of the high load involved. Furthermore since here the balers comprise of large structural elements of which the production tolerances are difficult to control, the required high accuracy measurements as necessary for a baler control system, are difficult to achieve.